Motor starting and protecting apparatus

ABSTRACT

A combination starting and protecting device particularly useful with split phase motors such as those used with refrigeration compressors is disclosed in which an element of material having a positive temperature coefficient (PTC) of resistivity characteristic and a thermally responsive switch are disposed in the same housing. A thermal coupling of a preselected value between the PTC element and the thermally responsive switch is provided so that a desired reset or &#34;off&#34; time is obtained for the thermally responsive switch without affecting the &#34;on&#34; time.

This is a continuation-in-part of application Ser. No. 642,858 filedDec. 22, 1975, now abandoned.

This invention relates to the starting and protecting of electric motorsand more particularly to the starting and protecting of split phasemotors commonly used with refrigerator compressors.

It is conventional to provide electro-mechanical relays for startingsuch motors and motor protectors for preventing damage to the motorsshould a fault condition occur. U.S. Pat. Nos. 3,099,732, 3,168,661 and3,248,627 disclose devices in which both relay and protector functionsare combined in a single package. Such a package facilitates simple andlow cost installation on motors to which they are to be connected andinsure that the motors are properly protected. The protectors in suchcombination packages typically comprise a bimetallic element throughwhich the motor current passes. The element is capable of assumingcontacts open and contacts closed positions depending upon thetemperature of the element. In order to provide protection against alltypes of fault conditions the protector must be sensitive to motortemperature as well as motor current. As set forth in the referencedpatents provision is made to either thermally isolate the protector fromthe relay so that they operate independently of one another so that anyheat produced by the relay will not adversely affect the calibration ofthe protector or, as disclosed in U.S. Pat. No. 3,248,627, to closelythermally couple the protector with relay coil so that the coil can actas an analog of the motor windings. That is, the coil carries the samecurrent as the main winding and thus I² R heat is generated in the coilin direct proportion to I² R heat generated in the main winding. Thislatter approach has limitations in its effectiveness since the thermalcapacity of the motor is so much greater than that of the relay.

More recently a more economical and reliable way to start split phasemotors has been developed which involves the use of positive temperaturecoefficient (PTC) of resistivity material electrically coupled to thestart winding. Upon initial energization the PTC material is in a coldor low resistance mode thereby permitting a relatively large current topass through the start winding. As the motor reaches its running speedthe PTC material heats up and goes into a high resistance modeeffectively deenergizing the start winding. An example of this type ofstarting device is set forth in British Patent Specification No.1,042,126. Protection of the motor in this system is providedseparately. As with the electro-mechanical relay and protectorcombination units it would be desirable to combine the starting andprotecting functions into the same device for reasons of economy.Further, it is desirable that the motor protector sense the temperatureof the compressor shell since the shell temperature is indicative of theinternal temperature of the compressor. The protector can follow theshell temperature more closely if it is not exposed to air currentssurrounding the compressor. The housing generally used to cover theterminals of the protector and starter would help shield the protectorfrom these air currents. However, when the protector is mounted on themotor casing as shown by the patents cited supra, other problems arepresented, particularly when used in compressor applications. That is,during normal operation of a refrigeration compressor there exists ahigh differential pressure between the evaporator and the condenser.When the compressor is deenergized some time is required for thepressures to equalize so that the torque required to turn the pumpdecreases to a level which is lower than the starting torque of themotor. In many domestic refrigerators this is in the order of a halfminute to five minutes. If restarting is attempted too soon afterdeenergization with the differential pressure still too high the motoracts as though it has a locked rotor and burn out of the winding canoccur unless effective protection is provided. When the rotor is lockedthe rate of temperature rise of the motor winding is much too fast tocause any appreciable temperature rise of the motor casing before thetemperature of the motor winding becomes excessive so that protectionwhich relies solely on sensing of the casing temperature is inadequate.Attempting start up during a locked rotor condition will result in anabnormally high current level being drawn in an attempt to develop thetorque necessary to overcome the starting load. If the motor casing isrelatively cool when the rotor becomes locked the protector may cyclemany times before the casing is heated sufficiently to contribute to theprotector's effectiveness by decreasing its on time and increasing itsoff time.

Thus it is desirable to increase the off time of the protector. Thiscould be done by reducing its reset temperature however this isundesirable for several reasons. First a lowered reset temperature couldcause the protector to stay off for too long a period of time when thecasing and ambient temperatures are high such as after a runningoverload has caused the protector to trip. Further, as the differential(between trip and reset temperature) of a motor protector disc iswidened its life is shortened. Mounting the PTC starter thermallyisolated from the protector, in the same manner as disclosed in U.S.Pat. Nos. 3,099,732 and 3,168,661 would not alleviate this problem. Onthe other hand since the PTC element in the starting device reaches arelatively constant temperature within a few milli-seconds it could notbe used as an analog in the manner taught by U.S. Pat. No. 3,248,627.

It is an object of this invention to provide a novel and improved solidstate motor starter and protector combination package, one which isparticularly adapted for use in starting and protecting split phaseelectrical motors used with compressors; to provide such a combinationpackage which is easily applied to different compressors and which is ofvery compact and economical construction; to provide such combinationpackages which facilitate easy mounting to a motor and ensures not onlyeffective starting but also complete protection.

Briefly, the present invention relates to a combination starting andprotecting device for an electric motor of the type having a main orrunning winding and an auxiliary or starting winding, commonly referredto as a split phase motor. The device includes an element of materialwhich has a resistance characteristic with a positive temperaturecoefficient (PTC) and a sharply defined anomaly or transitiontemperature above which the elements resistance increases sharply. Thedevice also includes a thermally responsive member such as a snapactingdisc mounting a movable contact and so arranged that upon an increase intemperature of the disc to a predetermined level, it will snap from acontacts closed to a contacts open configuration. The disc iselectrically coupled to line current so that snapping of the disc to theopen contacts configuration deenergizes the motor. The thermallyresponsive member is thermally coupled to the PTC element which heats upto its operating temperature almost instantaneously when power isapplied and thereby supplies a heat reservoir which furnishes heat tothe thermally responsive member when power is removed increasing the offtime of the member. Thus the disc is maintained in its contacts openconfiguration for a preselected extended period of time allowing themotor and the PTC element to cool to a desired level.

The invention accordingly comprises the construction hereinafterdescribed, the scope of the invention being indicated in the appendedclaims.

In the accompanying drawings, in wich several of various possibleembodiments of the invention are illustrated:

FIG. 1 is a perspective view of a starter/protector combination devicemade in accordance with the invention;

FIG. 2 is a side view of the FIG. 1 device with the starter portionshown in cross-section along lines 2--2 of FIG. 1;

FIG. 3 is a front view of the FIG. 1 device with the protector portionshown in cross-section along lines 3--3 of FIG. 1;

FIG. 4 is a schematic circuit diagram of the FIG. 1 embodiment employedwith a split phase motor; and

FIG. 5 is a schematic circuit diagram similar to FIG. 4 but of analternative embodiment of this invention.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

Referring now to FIGS. 1-3 a motor protector/starter package made inaccordance with the invention is identified by reference numeral 10comprising a motor protector portion 12 and a starter portion 14. Asbest seen in FIG. 3, motor protector 14 comprises and electrically andthermally conductive housing or can 16 formed of any suitable materialsuch as low carbon steel having a top wall and depending side walls 18forming a cavity therein. Attached to the free end of side walls 18around the perimeter is an outwardly extending flange 20. A lip portion22 is provided on two opposite sides which is bent over to clampinglyengage a lid 24. Interposed between can 16 and lid 24 is an electricallyinsulative gasket 26 to electrically separate lid 24 from the can 16. Asseen in FIG. 1, gasket 26 is folded around two opposite edges of lid 24.A terminal 28 is electrically connected to can 16 by welding or othersuitable means and is formed into a connector sleeve 30 (see FIG. 1)aligned with other connector sleeves from relay 14 to be discussedinfra. Another terminal 32 of the bayonet variety is electricallyconnected, as by welding, to lid 24.

Attached, as by welding, to the top wall of can 16 is a stationarycontact 34 made from a material of high electrical conductivity such assilver. Positioned to be movable into and out of engagement withstationary contact 34 is a movable contact 36 preferably made from thesame material as contact 34. Movable contact 36 is welded or otherwisesecured at one end of a thermally responsive bimetallic member 38, suchas a dish-shaped member having one layer of metal of a low thermalcoefficient of expansion and another layer of metal of a relativelyhigher thermal coefficient of expansion so that upon heating and coolingof member 38 it will snap between a first configuration in whichcontacts 34, 36 are in engagement as seen in FIG. 3 and a secondconfiguration in which contacts 34, 36 are out of engagement.

The end of member 38 opposite contact 36 is suitably attached incantilever fashion by welding to a flat heater element. A welding slug42 is conveniently employed to mount bimetallic member 38 to an end ofheater 40 but slightly spaced therefrom. A dimple 44 is formed in heater40 and acts as a stop for bimetallic member 38. Heater 40 is formed ofany one of a variety of materials of selected electrical conductivity sothat the element is adapted to generate a predetermined amount of heatin response to a selected flow of electrical current therethrough. Forexample, heater element 40 may be formed of rigid cold-rolled steel toprovide the element with stability and selected electrical heatingcharacteristics.

Lid 24 is formed with two indented portions, portion 48 serving as amount for the heater 40 to which it is attached as by welding. Indentedportion 46 serves to position the mounted end of the bimetallic memberin a desired location relative to stationary contact 34. Gasket 26 isprovided with a cut out portion through which indented portion 48 of lid24 extends.

Protector 12 is calibrated by bending can 16 at stationary contact 34until the desired force is exerted on movable contact 36. The free endof heater 40 is in close physical proximity to indented portion 46 oflid 24 covered by gasket 26. This facilitates calibration since themounted end of the bimetallic member 38 is kept from moving while can 16is being bent. Further information on a motor protector of the typedescribed above may be found in U.S. application Ser. No. 535,634 filedJan. 10, 1975, which issued Mar. 29, 1977 as U.S. Pat. No. 4,015,229 andis assigned to the assignee of the instant application.

Relay or starter portion 14 comprises a generally cup-shaped casing 50having a top and a depending side wall 52 forming a casing cavity whichis open at one end and which has a groove 54 extending around the openend. As shown, the casing rim preferably has a slotted portion indicatedby the slots 56 and 58. Preferably the casing has an additional wall 60depending from the casing top in spaced adjacent relation to the slottedportion of the casing. The casing 50 is formed of an electricallyinsulative or dielectric material and is preferably formed of arelatively rigid material such as a thermoplastic polyester or the like.

A first electrically conductive metal terminal 62, preferably formed ofstiffly resilient material such as plated phosphor bronze, berylliumcopper, steel or the like is disposed within the casing 50. As shown,the first terminal preferably has a plate portion 64 provided with aplurality of raised projections 66 thereon and has integral spring legs68 extending upwardly from the plate portion 64 to resiliently bearagainst the casing top. The first terminal has a connector portion 70extending through the casing sidewall. Preferably, for example, theconnector portion 70 is integral with the plate portion of the terminaland has the form of a metal sleeve of selected length connected to theplate portion 64 by an intermediate connector part 72 and split, asindicated at 74, one end 76 of the sleeve being engaged with theadditional wall 60 of the casing for locating the terminal laterallywithin the casing with the sleeve extending through slot 58 in thecasing sidewall.

A resistor element 78 is also disposed within the casing cavity.Preferably the resistor element 78 is formed of a ceramic material suchas lanthanum-doped barium titanate having a positive temperaturecoefficient of resistivity. Preferably the selected material is adaptedto be self-heated by directing electrical current through the resistormaterial and is adapted to display a sharp and very large increase inelectrical resistance when heated to a selected temperature for reducingcurrent flow through the material to a very low level and for therebylimiting the heating of said resistor material to approximately thatselected temperature level. As shown, the resistor element 78 ispreferably in disc form and has contact surfaces 80 and 82 formedthereon by metallizing or the like in any conventional manner forfacilitating electrical contact to the resistor element. The contactsurface 82 of the resistor element is disposed on the projections 66 onthe first terminal 62 in electrical engagement with that terminal.

The solid state starter portion 14 further includes a secondelectrically conductive metal terminal 84. The second terminal 84 has aplate portion 86 which rests on the casing shoulder or groove 54 asshown in FIG. 2 for closing the opening end of the casing. As shown, theplate portion 86 has a plurality of projections 88 formed thereon forelectrically engaging the contact surface 80 of the resistive element78. The second terminal also has a connector portion 90, preferably inthe form of a metal sleeve split at 92 and welded or otherwise connectedto the terminal plate portion 86 and extending through the casing slot56, the connector sleeve 90 also having an end engaged by the additionalwall 60 of the casing for assisting in locating the second terminalrelative to the casing. As shown, particularly in FIG. 1, the secondterminal 84 preferably has a down turned flange portion 94 having one ormore blade terminals, such as blade 96 extending from the flange spacebelow the plate portion of the terminal 84.

Further information on a solid state starter of the type described abovemay be found in U.S. application Ser. No. 528,066 filed Nov. 29, 1974,which issued on Nov. 18, 1975 as U.S. Pat. No. 3,921,117 and is assignedto the assignee of the instant invention.

The PTC element tends to stabilize the air temperature within the casingwith the result that the protector can sense compressor heat moreeffectively because of its juxtaposition to the compressor shell and itselectrical connections to the header.

Motor protector portion 12 is affixed to starter portion 14 so that apreselected thermal path 98 exists between PTC element 78 andthermostatic member 38. Since the PTC element heats up to its operatingtemperature almost instantaneously when power is applied it serves as aheat reservoir which furnishes heat to the thermostatic member 38 of theprotector when power is removed and increases the off time of theprotector. For a resistive element 78 having a mass of 5.8 grams athermal resistance of between approximately 5°-9° C./watt between theresistor element 78 and protector can 16 will result in a satisfactoryreset time. Preferably, the thermal resistance should be approximately7° C./watt which results in between approximately half a minute and 3minutes rest which permits the compressor pressures to equalizesufficiently to permit restarting and provides sufficiently long offtime to avoid the deleterious results mentioned supra. It will beunderstood that the thermal resistance between the resistor element 78and the thermostatic element 38 can be readily adjusted by interposingtherebetween selected thermal conductors or carriers.

The particular construction shown in the drawings and with theaforementioned element 78 of 5.8 grams, had a thermal capacitance of2.87 watt sec/° C. and casing 50 had a thermal capacitance of 2.6 wattsec/° C. The thermal capacities of the various elements may be varied toprovide optimum performance for a particular compressor.

Another way of defining thermal path 98 between resistor element 78 andthermostatic element 38 in accordance with this invention is to compareit with the change in off time of thermostatic element 38 when thethermal resistance of path 98 approaches infinity, e.g. when the PTCstarter is thermally isolated from the protector as disclosed in theaforementioned U.S. Pat. Nos. 3,099,732 and 3,168,661, under a conditionof locked rotor. The off time will be increased from 50% to 300%pursuant to the invention versus the same resistor element and protectorwith a thermal resistance of infinity therebetween. In addition, understeady state conditions of compressor operation the thermal resistanceof path 98 and the thermal capacity of resistor element 78 is adjustedso that the increase in effective ambient temperature in the vicinity ofthe thermostatic element 38 is raised not less than 10° C. and not morethan 60° C.

FIGS. 4 and 5 show two ways the combination motor protector starter 10can be employed with a typical split-phase motor having a start windingSW and a main winding MW. As seen in FIG. 4, line L2 is connected toterminal 96, one side of PTC element 78 and main winding terminal 84.The other side of PTC element 78 is connected to start winding terminal62. The other side of the windings are connected to terminal 30 of motorprotector portion 12. Line L1 is connected to terminal 32 of motorprotector portion 12. Thus, upon initial energization PTC element 78 isat ambient temperature and therefore has a relatively low level ofresistance. Current is allowed to pass through both windings MW and SWuntil the I² R heating in PTC element 78 causes its temperature toincrease above its anomaly point above which point its resistancesuddenly increases to a high level effectively deenergizing the startwinding SW. Current continues flowing through the main windingthermostatic member 38 and heater 40. Heater 40 is not always necessary,however, it is generally employed since it is beneficial in making theprotector current sensitive. Should an overload occur, either throughlocked rotor, overcurrent, etc., thermostatic member 38 will move to itsopen contacts configuration thereby deenergizing the motor. Except forthe few milliseconds during starting when PTC element 78 is at atemperature below its anomaly it is maintained at a relatively high andconstant temperature. Since the mass of element 78 is substantial itconstitutes a heat reservoir. When power is removed from the circuit(e.g. when contacts 34, 36 open) the heat from the reservoir flows tomember 38 via thermal path 98 maintaining member 38 above its resettemperature for an extended period of time keeping it in its opencontacts configuration for a given period of time while the motor has achance to cool off and the compressor pressures balance. This will be onthe order of 0.5-3 minutes or more if locked rotor conditions persist.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

I claim:
 1. A combination motor starter and protector apparatuscomprising:a starter portion including a housing, terminal means mountedin the housing for connecting a motor starter and protector apparatus toa motor and a source of power, an element composed of positivetemperature coefficient (PTC) of resistivity material disposed in thehousing, electrical lead means connecting the element to the terminalmeans, a protector portion including first and second electricalcontacts disposed in the housing electrically connected to the terminalmeans, the contacts movable relative to one another into and out ofengagement, a thermostatic member disposed in the housing andoperatively connected to the set of contacts, the thermostatic memberadapted to move from a first configuration in which the contacts are inengagement to a second configuration in which the contacts are out ofengagement and back to the first configuration, the contacts interposedbetween the source of power and the motor so that when the contacts areout of engagement the motor is deenergized, and selected thermalresistance means .Iadd.between approximately 5°-9° C./watt disposed.Iaddend.between the PTC element and the protector portion.
 2. Apparatusaccording to claim 1 in which the thermostatic member is a snap actingbimetallic member having a free end portion and one of the first andsecond electrical contacts is contact mounted on the free end portion..[.3. Apparatus according to claim 1 in which the said thermalresistance is between approximately 5°-9° C./watt..].
 4. Apparatusaccording to claim .[.3.]. .Iadd.1 .Iaddend.in which the said thermalresistance is approximately 7° C./watt.
 5. Apparatus according to claim1 further including a heater disposed in the housing, the heaterthermally coupled to the thermostatic member.
 6. Apparatus according toclaim 1 in which the thermostatic member is serially connected to thePTC element.
 7. Apparatus according to claim 1 in which the terminalmeans includes connectors adapted to connect the thermostatic element toone power line and the PTC element to another power line.
 8. Apparatusaccording to claim 6 further including a heater serially connected tothe thermostatic member.
 9. Apparatus according to claim 1 furtherincluding a heater physically interposed between the thermostatic memberand the PTC element.
 10. Refrigeration apparatus comprising acompressor, a motor having a start and a run winding for driving thecompressor, an element composed of material having a positivetemperature coefficient (PTC) of resistivity above an anomalytemperature, the element coupled to the start winding, means to connectthe element to a source of power so that upon energization of theelement a relatively large inrush of current flows through the elementand the start winding for several milliseconds until heat internallygenerated within the element raises the temperature of the element abovethe anomaly temperature, the concomitant rise in resistance effectivelycutting off current flow through the element and the start winding, aprotector comprising a movable and a stationary contact, a thermostaticmember having a set and a reset temperature operatively connected to themovable contact and adapted to move the movable contact into and out ofengagement with the stationary contact when it rises to the settemperature and falls to the reset temperature respectively, thecontacts interposed between the source of power and the motor so thatupon disengagement of the contacts the motor is deenergized, the PTCelement and the protector being thermally coupled to one another with aselected thermal resistance .Iadd.between approximately 5°-9°C./watt.Iaddend., the PTC element having a substantial thermal masswhereby upon deenergization of the motor heat will flow to the protectorkeeping the thermostatic member above its reset temperature for anextended period of time. .[.11. Refrigeration apparatus according toclaim 10 in which the thermal resistance is between approximately 5°-9°C./watt..].
 12. Refrigeration apparatus according to claim .[.11.]..Iadd.10 .Iaddend.in which the thermal resistance is approximately 7°C./watt.
 13. In a motor protector having a thermostatic element movablefrom a contacts closed position to a contacts open position at a givenfirst temperature of the element to thereby deenergize a motor coupledto this protector and interrupt heat generated in the motor and movablefrom the contacts open position to a contacts closed position at a givensecond temperature to thereby reenergize a motor coupled to thisprotector, the second temperature lower than the first temperature themethod of increasing time required for the element to cool from thefirst temperature to the second temperature comprising the steps ofselecting a resistor having a steeply sloped positive temperaturecoefficient of resistivity at temperatures above an anomaly, providing asource of power for the resistor, and thermally coupling the resistor tothe thermostatic element .Iadd.with a thermal resistance betweenapproximately 5°-9° C./watt.Iaddend.. The method according to claim 13including adjusting the thermal coupling of the resistor and thethermostatic element to increase the time required for the element tocool and the thermal capacity of the resistor from the first temperatureto the second temperature within a range from 50% to 300% compared tothe resistor element having essentially no thermal coupling with thethermostatic element.
 15. The method according to claim 13 includingadjusting the thermal coupling of the resistor and the thermostaticelement so that the ambient temperature in the vicinity of thethermostatic element under steady state conditions of operating israised not less than 10° C. and not more than 60° C. compared to athermostatic element having essentially no thermal coupling with aresistor element.